Slide-scale.



Patented luly I, |902.

J. S. MEBRITT.

SLIDE SCALE.

(Application med un. '5, 1901.)

2 'Sheets-Sheet 2.

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UNITEDI STATES PATENT OFFICE.

JAMES S. MERRITT, OF PHILADELPHIA, PENNSYLVANIA.

SLIDE-SCALE.,

SPECIFICATION forming part of Letters Patent No. 703,437, dated July 1, 1902.

Application filed March 5, 1901.

.'ZO rtl/ whom it may concern:

Be it known that I, JAMES S. MERRITT, of the city and county of Philadelphia, Pennsylvania, have invented an Improvement in Slide-Scales, of which the following is a speciiication.

My invention relates to slide or calculating scales and is fully set forth in the following specification and shown in the accompanying drawings.

Itis the object of my invention to provide a scale or rule for calculating beam sections, loads, spans, duc., by which with some factors given the others may be ascertained without I the necessity of calculation or reference to tables.

Two sets of scales are used in making the calculations involved in the solution ofthe problems to which my invention relates, of which one set is adapted for calculating the load per square foot over the area supported by a beam of any depth and weight ofany span and spacing distance, so that with any three of the factors given the fourth may be readily ascertained, and the other set is adapted for calculating` the total loadvfor a beam of any section, of any span, and with any method of supporting and loading, so that with any three of the factors given the fourth may be obtained. Y

My invention relates to the combination of these two sets of scales in such a manner that leither set of scales may be used with a common scale expressing the factor of the beam weights and sections.

In carrying out my invention I employ a series of scales indicating the factors laid out in distances proportional to the logarithms of each series of factors, certain scales being movable with reference to others, so that their adjustment will effect an addition'or subtraction of thelogarithms of the factors according to the well-known formulte for calculating loads, dsc.

My inventionis fully illustrated in the accompanying drawings, in whichw i Figure l is a plan view of my calculatingscale, showing the same in use for a calculation in which the load per square foot and the spacing distance are part of the factors employed. Fig. 2 is a similar view illustrating the same in use for a calculation in Serial No. 49,686. (No model.)

which the load in tous and manner of supporting and loading are part of the factors employed, and Fig. 3 is a crosssectional view on the line :c @c of Fig. 2.

The scale consists of two parts d and b, having a movement with reference to one another, each part containing scales of part of the factors so arranged with -referen ce to one another that their relative movements will have the effect of` the addition or subtraction of the logarithms of the adjacent numbers in the manner well known in the construction of slide-rules. The particular manner of constructing and combining the two parts d and b is of course immaterial, provided they have the requisite movement with respect to one another'. As shown, the part a consists of a flat piece havinga central longitudinal guideway c, in which the part b is carried and may be moved longitudinally in guides d d.

The particular location or order of the scales is not material, provided they are so arranged with reference to one another that their relative movements will correspond with the mathematical calculations indicated by the formulte. l

As shown, the scales A and E are arranged at opposite ends of the upper portion of the part ct and scales D and G at opposite ends of the lower portion. A scale B at the upper portion of the part l) extends the length of the part ZJ and is common to both scales A and E, and scales C and F are arranged at the opposite ends of the lower portion of the part l). The scales A, B, C, and D are used for one set of calculations and the scales E, B, F, and G for another. These scales A, B, C, and D are designed for use in calculations in which the load por square foot, the beamsection, the distance between beams, and the span are factors and are based upon the formula \V d I., in which c equals the coefcient of the beam-section--zl c., the net load IOO of the beam, and CZ equals the distance in feet between the centers of parallel beams. Scale A represents the load in pounds per square foot (IV) and is laid olf in distances equal to the logarithms of the numbers given, according to the well-known method employed in sliderules. The only numbers given on scale A are those loads that would be met with in ordinary practice-e. g., from iit'ty pounds to four hundred pounds. Scale B represents the beam-sections as usually described by their depth in inches and their weight in pounds per foot and is laid off in distances equal to the logarithms of the coefficients of the standard beam-sections (c) of the given depths and weights. For example, the coeficient of a standard twenty-one-pound nineinch beam is two hundred thousand. The graduation for this beam is therefore laid off at a distance equal to logarithms two hundred thousand. Scale C represents the distances in feet between the centers of parallel beams (d) and is laid off in distances equal to the logarithms of the numbers in the same manner as the scale A. In fact, A and C are two parts of the same scale, the logarithmic distances of the smaller numbers (l to 30) being given in the scale Gand the distances of the larger n umbers 50 to LIOO beinggivenin the scale A. Scale D represents the span of the beams in feet (l) and is laid olli' in double the distances ot the scales A or C and in the opposite direction.

From the formula: (Z W l or xxi/,l (Z Y2 we obtain the formula log. c log. IV/ (t 2 log. l.

'lhe movement. of the scale B with reference to the scale A is equivalent to the subtraction of logarithm W' from logarithm c, and as the scale C is the same as scale A and scale D the double of scale C reversed it follows that the correspondingmovement ofthe scale C is equivalent to the addition of logarithm d and 2 logarithm l.. This addition of twice logarithm Z is due to the fact that the scale D is laid oit' in twice the logarithmic distances of the scales A and C and in the oppo site direction.

Having any three factors given, the fourth may readily be found. Suppose, for example, that the given conditions required a tWenty-ive-foot span with the beams spaced six and one-half feet apart capable of sustaining a load of fifty pounds to the square foot. To ascertain the proper beam-section for these conditions, scale C is moved until the graduation 615 is over the graduation .25 in scale D. Then under graduation 50 in scale A will be found the proper beam weight and section in scale B, which in this case is a nine-inch twenty-one-pound beam.

Under the scale D may be arranged a series of numbers indicating depths of beamsections placed under the appropriate spans, which must not be exceeded in the case of plastered ceilings. This is a feature, howlog.

ever, which forms no essential part of the slide-rule and may be omitted.

So far as calculations with the safe load in pounds per square foot, the beam Weight and depth, the spacing and span as factors are concerned the scales A B C D are suflieient. It is equally desirable, however, to calculate with the total safe load in net tons, the beam weight and depth, the span and the manner of loading as factors, and for this purpose I provide the scales E, B, F, and G. As it is desirable that both slide-rules should be in one structure, I have combined them in a single rule, so arranging them that the single scale B may be used with either scale. This is accomplished by arranging 'the scales A, C, and D at one end and the scales E, F, and G at the other, with the scale B common to both.

The scales E, B, F, and G are based upon the formula iV,` in which the val- SOOO Z fr ues of c and Y, are those already given. VL equals the total load in net tons ol' two thousand pounds which will produce the given unit strain in the eXtreme fibers of a beam of given section with the given span and given manner of loading and supporting the beam, and r equals the ratio of bending moments for the different manners of supporting and loading the beams. The scale E represents the total safe load in net tons (lift) and is laid olf in distances proportional to the logarithms of the numbers. The scale F represents the manner of supporting and loading and is laid off in distances proportional to the logarithms of the ratios of the bending moments (fr) for the given methods of loading and support. The scale G represents the span (l) and is laid off in distances equal to the logarithms of the numbers, but in the opposite direction `from the other scales.

In lay-.ing out the scales It, F, and G with reference to the scale B, I proceed as follows: I ii rst arbitrarily select in the scale B some beam section and weight-e. g., a nine-inch twenty-one-pound beam. The coefficient of this beam-section is two hundred thousand, and from the formula Taking the value of fr as the unit in the scale of the ratio of bending moments-i. c., for a beam supported at both ends and uniformly loaded equals Z and l equals a'teirl'oot span-l obtain VL I m-w or IO.

This Oives the i 1o D total load in tous for a ten-foot span twentyone-inch nine-pound beam supported at both ends with the Weight uniformly distributed.

IOO

IIO

I therefore mark the number l0 on the scale E opposite the graduation 9 inch 211D. on the scaleB and place the point 2 (indicating the unit in the scale of the ratio of bending moments) on the scale F opposite to the point l0 (indicating the span) on the scale Having thus ascertained the proper location of the points l0 and l0 in the scales E and G, the other graduations are laid off in distances equal to the logarithms of the numbers, the direction of the scale G being reversed, as stated. Having thus laid off the scales E and G, the scale F is completed as follows: The point 2, as stated., represents the bending moment in the case of a beam supported at both ends, with the load uniformly distributed. lt also represents the bending moment for a beam supported at one end and fixed at the other, with the load uniformly distributed, and for one fixed at both ends, with the load applied at the center. lt is taken as the unit, with l for the value of r. The point l represents the bending moment for a beam fixed at both ends, with the load uniformly distributed, and the value of r is .667. The point 3 represents the bending moment for a beam supported at one end and fixed at the other, with the load applied at the center, and the value of o' is 1.5. For the point 4E the beam is supported at both ends and the load is applied at the center, with the value of 7:2. For 5 the beam is fixed at one end (cantaliver) and the load is uniformly distributed, with the value of 71:4. For 6 the beam is fixed at one end (cantaliver) and the load is applied at the other end, with the value of 71:8. The ratio of the factor o for these different methods of loading is .607, one, 1.5, two, four, eight. The points 1, 3, 4, 5, and 67 are therefore laid. out at distances equal to the logarithms of these values with reference to the point 2 as the unit.

The numbers l to 6 on the scale F are used arbitrarily to designate the various divisions 0f the scale and have no numerical significance.

The method of using the scales E, B, F, and G is as follows: From the formula c u 200011n O1 2000 WT5 we obtain the logarithmic formula: log. clog. 2000-log. /Vtzlog. Z-l-log. r. 'lhc movement of the scale B with reference to the scale E is equivalent to the subtraction of both the logarithm Wt and logarithm 2000 from the logarithm o, because in laying out the scale E (logarithm VJD) according to the formula the logarithm 2000, being constant in the equation, was subtracted. The formula WV, as given above was obtained by dividing the selected value of c-z'. e., two hundred thousand-by the constant two thousand, which is equivalent to the subtraction of logarithm 2000 from logarithm c. Consequently the positionsoecupied by the logarithmic values of Wt and Z in the scales and G with reference to the scale B are those obtained after the subtraction of the constantlogarithm 2000. The resulting movement ofthe scales F and G is equivalent to the addition of the logarithm i' and logarithm Z, the direction of the scale G being reversed.

`With any three factors given the fourth may be obtained by the proper adjustment of the scales. Thus in the example shown if it is desired to ascertain the proper span to be used with a seven-inch fifteen-pound beam supported at both ends and capable of sustaining a safe load of five and one-half tons applied at the center the scale B is moved until the point 7, l5 lb.77 is under 5i in scale E, and under the point 4C in scale F, which indicates the manner of support and loading, will be found the desired factor-4I. e. a five-foot span.

It will be understood that the selection of the values of the factors c and Zin laying out the scales E, F, and G is lpurely arbitrary, and other Values than those used maybe emn ployed without affecting the result.

Not only is it possible to iind any unknown factor when three are given, but with certain two factors given the others may be ascertained. Thus with scales A, B, C, and D, if the conditions require the use of given beams-e. r ten inches,tWenty-five poundsto sustain a given safe load of sixty-five pounds per square foot the adjustment of the scales A and B will indicate in scales C and D the various spans and spacings that may be used. So with the scales E, B, F, and G, if the conditions require a span of fifteen feet with the beam fixed at both ends and the load uniformlydistributed (r2.667) the adjustment of the point 1 in scale F over the point l5 in scale G will indicate in the scales E and B the total safe loads and beams of which such conditions will permit the use.

What l claim as new and desire to secure by Letters Patent is as follows:

l. A scale for calculating load, section, spacing, span and manner of supporting and loading beams, consisting of two members movable with respect to one another, onevof said members having' at one end a scale in dicating lthe loads in pounds per square foot laid off in distances proportional to the loga ritlims of the factors and a scale indicating the span laid off in distances proportional to twice the logarithms of the numbers and in the opposite direction to the scale of loads, and at the other end a logarithmic scale .in-a dicating the totali loads in net tons and a scale indicating the span laid off in distances proportional to the logarithms of the numbers and in the opposite direction to said scale of loads in tous, and the other member` having a scale indicating the beam-sections laid off in distances proportional to the logarithms of the coefficient of said beams and common to both the scales of loads and also having at one end a logaritlnnic scale indi- IOO 1o of said factors and a scale movable With rofl erence to one or more of the other scales in each series and common to both seri s of scales laid off in distances proportional to the coefficients of beams of given sections.

In testimony of which invention I have if;

hereunto set my hand.

JAMES S. MERRTT. Witnesses:

ERNEST HOWARD HUNTER, WILLIAM Il. FLANDERS. 

